shock!! no trip!

[eganelectrical]

When I wired my ccu I fitted all rcbo's. and tested all trip times etc. all passed!! In the garden mixing cement a few weeks later and water got all around the extension lead near the plugs! I didn't see this because it started getting dark! But Jesus I felt it with a rattle as I unplugged the mixer!
Went in the house and Rcbo for outside sockets still on! Checked trip times the next day and all still fine!! Surely this should have tripped??

 

[partypest]

I remember my lecturer explaining all of this, and it made perfect sense at the time because he was very good. However, age, kids, work and alcohol have made all the details go a bit fuzzy. What I do remember, is that it takes around 50mA to cause fibrillation in most people and the 30mA limit is to take allowance for the percentage of weaker people, like children etc. the time factor was also to do with fibrillation, and he did an amazing comparative drawing showing the electrical impulse for the heart and a 50Hz waveform. At no point did he say that safe and painless were the same thing.

 

[snowhead]

and the trip didn't go out then hes kinda lucky? yes?

Yes.

10ma is the ideal, shouldn't ever kill anyone.
30ma is the compromise, probability of death is extemely low, it would have to be the wrong person in the wrong situation at the wrong time.

No doubt if you stuck L and E directly either side of most peoples' heart on a 30ma, most people would have serious heart problems, I suspect the majority would die if no medical attention was given and the Rcd probably wouldn't trip.

I have and I'm sure plenty of other pople who work with electricity on a daily basis have had shocks. In theory we should all be dead, almost all of mine have been across the back of the hand or arm as I posted earlier only 1 across body and that's in 45 years of employment and a few years before that (I was an inquisitive child)

 

[partypest]

I was such an inquisitive child as far as electricity was concerned, I should be dead. Maybe I've become immune to it? I'll just fetch a screwdriver and find out.

 

[snowhead]

I was such an inquisitive child as far as electricity was concerned, I should be dead. Maybe I've become immune to it? I'll just fetch a screwdriver and find out.

When i was 10 / 11 I made up several extension leads with 2 pin male female connectors for train set power supplies, record player etc.
I had all the plugs with live pins exposed, you don't do Elec regs when your still in Junior school.
Minor shocks were the norm.

 

[Guitarist]

If you bridge L-N with your chubbly little fingers, without allowing any leakage to earth, how can the RCD know? Still gonna hurt though...

RCD's are not a magic cure-all.

 

[44ALLAN]

Well call me a wuss if you like but I wear disposable rubber gloves on every job I do.............not ideal but a little bit of extra protection just in case.
Keeps my fingernails nice and clean too

 

[Guitarist]

Well call me a wuss if you like but I wear disposable rubber gloves on every job I do.............not ideal but a little bit of extra protection just in case.
Keeps my fingernails nice and clean too

Not a wuss mate. As a classical guitarist, I wear gloves a lot of the time too....tho not to protect me from shocks.

 

[44ALLAN]

Not a wuss mate. As a classical guitarist, I wear gloves a lot of the time too....tho not to protect me from shocks.

I've got a Marshall 4x12 Bass Amp and Musicman Bass guitar here beside me.............fancy knocking a song or 2 out?
You play it I'll do the melody

 

[Engineer54]

Basically I have been told by an engineer and a rep from a RCBO manufacturer that they don't recommend more than 3 PC s on a trip, their thinking is on average with the monitor a computer can leak 2.5MAs, this has confused me and I have asked why, basically on one Job I have just done we had to install 6 ring mains in one room for 18 computers in Dado trunking, each of the 6 circuits rcbo protected, crazy?? well apparently they recommend 3 max per trip due to nusience tripping. I don't get this myself, your an engineer perhaps you can help me with it. then theres the 10MA situation, a couple of weeks ago there was a good thread about what amount of current actually kills you, I have heard 10MA, but always thought 30 MA, however a fair few sparks here said they had heard it was 10MA, if so and the OPs trip didn't go out when he took a whack I was wondering why it didn't go out, I asked for test results, he gave them, good readings, so, if a trip according to a manufacturer shouldn't have more than 3 computers on it due to nusience tripping and the death value apparently 10MA, and the trip didn't go out then hes kinda lucky? yes?

I was only interested in this statement...

A 30 ma trip should trip at 30% of the rating under fault conditions

​

An RCD has specific tripping characteristics for both fault and normal tripping for both mA and time. Never heard of this ''should at 30% of it's rating in a fault condition''.

As for the amount of PC stations on a RCD/RCBO, i've never had problems limiting such numbers to 5 stations. 3 seems to be a little OTT to me lol!!

The lethal current required, depends on too many factors and conditions to give a specific figure. and was all basically covered in that thread. 10mA is the RCD rating i use to protect communal shower room installations, and other higher risk areas throughout the hospital medical areas etc!!


As far as i can remember, 0.5mA = little sensation. 10mA = threshold of muscular contraction. 30mA = threshold of respiratory paralysis. 75mA = irreversible threshold of heart fibrillation. 1A = heart arrest!!
That's basically what i have always gone by anyway... lol!!

 

[Guitarist]

If you ramp test most 30mA RCD's, you'll find they trip in the early 20's, so more like 2/3rds.

 

[HandySparks]

If you bridge L-N with your chubbly little fingers, without allowing any leakage to earth, how can the RCD know? Still gonna hurt though...

RCD's are not a magic cure-all.

Just reading through the threads, and I was wondering whether someone was going to make this point. The OP, and almost everyone else is assuming a L-E fault path. If the fault is L-N, via the wet connector and the OP's fingers, the RCD function is irrelevant. So the OP may have had much more than 30mA through his hand without tripping the overcurrent protection. I guess that the level of current (if any) through his heart was low enough not to kill him.

 

[Engineer54]

If you ramp test most 30mA RCD's, you'll find they trip in the early 20's, so more like 2/3rds.

Agreed, but there are set out requirements that an RCD must meet on tripping mA. For example, must trip between X mA and Y mA (can't remember the mA ratings lol!!) to meet the BS standard!! Fault conditions are taken care of by faster tripping times...

....It's late here!! lol!!

 

[AndyOz]

An extract from a paper written by the IEEE is as follows:

Low-frequency electric currents of a few milliamperes flowing through the body cause muscular contractions. In the arm such an effect may make a subject unable to let go of a live conductor. The highest currents which 99.5 percent of men and 99.5 percent of women are able to let go have been shown to be 9 and 6 mA, respectively. Currents somewhat larger than this, in the range of 20 to 40 mA, passing across the chest may arrest respiration leading to asphyxia, unconsciousness, and even death. The most common cause of death in electric shock probably is ventricular fibrillation, a condition in which the circulation is arrested and death ensues very rapidly. An analysis of available experimental data indicates that body weight and shock duration are important factors in determining the maximum current not likely to cause ventricular fibrillation. Taking a weight of 50 kg as the average for a human victim it is suggested that the relationship between current shock duration is given by I = 116/??7, where I is the current in milliamperes and T is the time in seconds. It must be stressed that this has only been shown to be valid within the range of 8 ms to 5 seconds. Currents flowing through the nerve centers controlling respiration may cause respiratory inhibition, which sometimes persists for a long time after the current has been interrupted.

 

[Deleted member 26818]

My understanding, is that 6mA across the heart is sufficient to cause it to cease operating.
30mA from one hand through the body to the other, would not necessarilly cause 6mA to flow across the heart.
Current tends to flow along the outside of a conductor, a property known as 'skin effect'.
This also why fine wire conductors have a greater CCC than solid conductors of the same CSA, there is a greater surface area for the current to travel along.
As for the OP's question, it could be as already suggested, that the fault was not to earth, but from Line to Neutral.

 

[eganelectrical]

If you bridge L-N with your chubbly little fingers, without allowing any leakage to earth, how can the RCD know? Still gonna hurt though...

RCD's are not a magic cure-all.

Just reading through the threads, and I was wondering whether someone was going to make this point. The OP, and almost everyone else is assuming a L-E fault path. If the fault is L-N, via the wet connector and the OP's fingers, the RCD function is irrelevant. So the OP may have had much more than 30mA through his hand without tripping the overcurrent protection. I guess that the level of current (if any) through his heart was low enough not to kill him.

I bridged my thumb And forefinger across live and neutral once on a switch fused spur!
Fingers smoking!!